Furnace propane consumption

[eddylives]

We are into the season of requiring heat in the trailer now lol.
I did a little research to try and figure out how long two 30lb cylinders of propane will last us and found this information.

4.24 lbs of propane equals one gallon

one gallon equals 92000 BTU

So here goes the calculation

30 lb /4.24 = 7 gallons and a bit.....times two 14 gallons plus

14 times 92000 = 12880000btu

1288000/40000btu furnace=32.2 hours of run time continuously

So does this calculation sound right? Assuming the furnace is 40K btu (I have no idea what it is) and the only appliance running off of the propane?

I am aware that the furnace cycles and the actual time it will last is variable to the outdoor temperature and temperature set for inside.

Thoughts?

 

[danemayer]

You're on track, but the run time depends on thermostat setting, ambient temperature, insulation, air leaks, heat transfer through windows, how often the door is opened and for how long, and other factors.

One thing to consider: if you let the tanks switch over automatically, you'll always end up with 2 empty tanks at 3AM when it's 10 below zero.

 

[dave10a]

You're on track, but the run time depends on thermostat setting, ambient temperature, insulation, air leaks, heat transfer through windows, how often the door is opened and for how long, and other factors.

One thing to consider: if you let the tanks switch over automatically, you'll always end up with 2 empty tanks at 3AM when it's 10 below zero.

Furnace efficiency is very important. Most RV furnaces are lucky if they are 80%. The R factor of RV is generally over-stated to a large degree. Only a few mfg's publish a zero and 100 degree rating with actual data. The furnace and A/C are most likely running a full capacity to achieve the publish numbers. Also it temperature in the belly must be considered when it is freezing outside to keep the water lines from freezing.

 

[Lou_and_Bette]

You're on track, but the run time depends on thermostat setting, ambient temperature, insulation, air leaks, heat transfer through windows, how often the door is opened and for how long, and other factors.

One thing to consider: if you let the tanks switch over automatically, you'll always end up with 2 empty tanks at 3AM when it's 10 below zero.

Unless you check at least once a day EVERY day. That’s what I do and have never run completely out of gas at any time of the day or night. If you only run off one tank at a time, don’t you have to get up “at 3 AM when it’s 10 below zero” to open the other tank when that one runs out?

 

[danemayer]

Unless you check at least once a day EVERY day. That’s what I do and have never run completely out of gas at any time of the day or night. If you only run off one tank at a time, don’t you have to get up “at 3 AM when it’s 10 below zero” to open the other tank when that one runs out?

I would check the tank being used by lifting it slightly to estimate how much propane remained. When it felt "light", I would switch tanks and get the light one filled. I usually went about 3 days before filling.

More recently, I went to an external 120 gallon tank for our winter stays.

Although we haven't taken the RV out for ski season the past 2 winters, we now have CheapHeat and run the furnace on electric all the time. Though the rig is winterized, I have the thermostat set at 40 to keep the interior protected just in case...

 

[eddylives]

As a rule I will always have spare propane with us when we go out......usually four 30s ......two in use and two ready to go
I also have a few 20s floating around in case of a real emergency lol

And yes I have shared the pain of changing bottles in the middle of the night in the rain and snow so I try hard to keep an eye on fuel levels lol

The main reason for this thread was to confirm the information i dug up to calculate was correct

I am also curious to know the consumption of the other propane run appliances in use around my site and plan to look up the BTU values of the fridge , hot water tank,BBQ and future purchase of an on demand hot water heater

Thanks for all your input

 

[sengli]

I installed that mopeka LP tank monitoring system on my rig last year. It works great. I know in a second or two, exactly how propane is in both of my monitored tanks. Just get out my smart phone, and open the app...and the tanks display everything I need.

 

[CLGray]

Re: Furnace propane consumption (-30* sustained weather)

Hello all,

Have been full timing a 43’ Heartland Road Warrior RW425 for about two years now. Just had my first experience with sub zero temperatures and it has been less than exciting.

We we have had -30* weather with wind chills at -60* for the last few days.

Have learned a few few valuable lessons I would like to share with the group.

• Propane liquifies and stops becoming useful if ingested below zero. We have been troubleshooting and had the furnace pushing cold air while running. Yes have laser gun and the air is 23*. This is different that running out of propane and having the furnace turn off because of low or no pressure.
• We have been through refills and fill tanks while outside temps are -20* thru -31* last night. No avail with new tanks. We did get a breakthrough with heating the tanks in the truck while not in use. They work great once in the car for a few hours. Just rotate them out. We have ordered cylinder heat blankets for the future. Heating tanks ensures that the LPG liquifies and keeps you with a nominal pressure.
• Installed subframe heaters to prevent freeze over and have allowed a water drip from all faucets while Grey water tanks are open.
• Installing 2” insulated foam to underframe this weekend with service ports to make it easier to work on things and keep it warm.
• Using insulated foam tubing for all water lines. Will install this weekend.
• With furnace set to 75* and two space heaters on we have a bedroom temp of 64* ( a 95* temperature increase from outside)

Any questions just let me know. Hope this helps anyone interested.

 

[danemayer]

allowed a water drip from all faucets while Grey water tanks are open.

Hi CLGray,

Thanks for sharing.

At temps like you're experiencing, the drip from the gray tanks could freeze as it goes into the sewer, leading to an ice dam building up into your sewer outlet.

If you're using foam board to create a skirt that protects the underbelly, and you put a heater into the enclosed area, it should keep your plumbing warm. It'll also prevent your gate valves from freezing. Raise the heater off the ground in case water runs under the RV.

If you haven't already done so, put a 60 watt drop light into the UDC to keep the water inlet from freezing. And hanging a heat lamp over the water pump area will also be helpful.

You probably have low-point drains. The water just above the drain valves needs to be kept from freezing. The skirt with heating should protect them.

Take a look at our Water Systems Winter Usage Guide for more tips.

 

[CLGray]

Hi CLGray,

Thanks for sharing.

At temps like you're experiencing, the drip from the gray tanks could freeze as it goes into the sewer, leading to an ice dam building up into your sewer outlet.

If you're using foam board to create a skirt that protects the underbelly, and you put a heater into the enclosed area, it should keep your plumbing warm. It'll also prevent your gate valves from freezing. Raise the heater off the ground in case water runs under the RV.

If you haven't already done so, put a 60 watt drop light into the UDC to keep the water inlet from freezing. And hanging a heat lamp over the water pump area will also be helpful.

You probably have low-point drains. The water just above the drain valves needs to be kept from freezing. The skirt with heating should protect them.

Take a look at our Water Systems Winter Usage Guide for more tips.

Thank you for the info. Thanks for allowing me on the forum.